This program project grant supports a clinical and laboratory program for a 20 bed intensive care ward devoted primarily to the treatment of hematologic malignancies by marrow transplantation. Total body irradiation and high dose chemotherapy are utilized to condition the patient to accept the graft and to eliminate malignant cell populations. Supportive facilities include granulocyte and platelet transfusions, laminar air flow isolation, gut sterilization and sterile diets. Immunologic recovery will be monitored by a variety of in vitro and in vivo tests. Research areas include prevention and treatment of graft-versus-host disease, studies of interstitial pneumonia and opportunistic viral infections, studies of in vitro hematopoiesis and studies of platelet immunology and physiology. Extensive histocompatibility studies of the patient and the family will be carried out in order to define the role of various HLA loci in the success or failure of engraftment. Monoclonal antibodies reacting with T-cells or T-cell subsets will be used in an effort to prevent and/or or treat graft-versus-host disease. Monoclonal antibodies reacting with leukemic cells will be used in an effort to prevent recurrence of leukemia after grafting. Supporting services and related research include: Pathology, Dietary, Microbiology, Cytogenetics, Pulmonary, Dental and Gastroenterology. Data Processing and Biostatistical support provide maximum utilization of information generated.